It has been consistently shown in the literature that when gaze is directed to a specific location, for a long enough duration, at the correct time relative to the motor execution, high-levels of performance are possible. In recent years, a particular gaze called quiet eye (QE) has gained growing attention among researchers investigating aiming tasks and has become accepted within the literature as a measure of optimal attentional control. Previous studies consistently displayed that longer QE is associated with superior performance however there is lack of understanding how QE exerts its positive effect on performance. Therefore the overriding aim of the current program of research was to explore the mechanisms behind the QE by experimentally manipulating the separate aspects of the QE definition in ways that have not been explored by previous researchers. In study 1 (Chapter 2), two experiments were conducted to examine the key characteristics of the QE in golf putting; duration and location. Novice participants were randomly allocated to training groups of experimentally longer or shorter QE durations (experiment 1) and training groups of different QE locations (experiment 2). A retention-pressure-retention design was adopted, and measures of performance and QE were recorded. All groups improved performance after training and the levels of performance achieved were robust in a pressure test. However there were no significant group effects. Study 1 provided partial support for the efficacy of QE training, but did not clarify how the QE itself underpins the performance advantage revealed in earlier studies and suggested that the QE should perhaps not be reported simply as a function of its duration or its location. In study 2 (Chapter 3) an examination of the timing of the QE was performed, using an occlusion paradigm. This provided an experimental manipulation of the availability of visual information during the putting action. Expert participants performed a putting task under three different conditions, namely full, early, and late vision conditions. The results showed that putting accuracy was the poorest when late visual information was occluded (early vision condition). Therefore study 2 suggested that the correct temporal placement of gaze might be more crucial to successful performance, and that putting accuracy was poorer when the latter component of QE which ensures precise control of movement was occluded. Previous research has revealed that anxiety can attenuate the QE duration, shortening the latter component which was shown to be important in study 2. Therefore the final study in the thesis examined the influence of anxiety on attentional control (QE). Expert golfers participated in a putting shootout competition designed to increase levels of anxiety and continued putting until a missed putt occurred. The results revealed that duration of QE was shorter on the missed putt, while there was no difference in QE duration for successful putts (first and penultimate putts). The results are therefore supportive of the predictions of attentional control theory. Furthermore this reduction in QE duration was result of latter component of QE being attenuated, supporting models of motor control that point to the importance of online visual information for regulating control of movements. The results of this series of studies conclude that the timing of the QE – maintaining a steady fixation through the unfolding movement to ensure precise online control - seems to be the strong candidate for how QE exerts a positive effect on performance.